Farming Southern bluefin tuna is currently the single most valuable sector of South Australia’s aquaculture industry. Over the past decade the farmed sector has grown to the point where around 98 per cent of the Australian southern bluefin tuna quota is now farmed. Farming is carried out by those operators who have access to part of the Australian quota and who possess the necessary farm lease sites, and the equipment and expertise to catch tuna. Quota is an entitlement, which can be sold or leased to other operators.
South Australia’s tuna industry has increased production significantly since 1995/96, now producing more than 9,000 tonnes of processed tuna, valued at over $260M.
Industry estimates that South Australia will be producing over 10,000 tonnes of tuna valued at over $300M by 2003/04. Australian farmed tuna is sold almost exclusively to the Japanese sashimi markets, however some growers are beginning to look further abroad to other markets such as the United States.
Tuna are caught in the Southern Ocean transferred to Port Lincoln and fattened in cages for between 3 – 5 months. Most of the tuna is sold frozen, under contracts, where lower prices are often paid compared to fresh fish, but without the uncertainty of market and auction price fluctuations at harvest time.
The fish are then fed a combination of high fat imported sardines, anchovies, mackerel, red bait, squid and locally caught high protein sardines.
A variety of feeding methods are used depending on the bait type to ensure each fish is fed appropriately. No chemicals or antibiotics of any type are used. The farmers monitor feed rates, fish activity, water temperature, wind and wave action, dissolved oxygen, net fouling and the sea floor and modify feeding practices to best suit the activity of the fish and state of the water column in and around the farm.
The pontoons and nets are designed to maximise water flow and minimise marine growth and are regularly monitored by dive teams.
In the winter months when the tuna have reached their optimal size and condition they are harvested under strict rules. The harvest process includes the physical capture of each individual fish and within seconds, the killing, bleeding and gill and gutting before the fish are placed in an ice slurry (0oC) and transported to factories for processing or to boats for “on board” freezing.
Each fish produced is certified by the Australian Government as meeting all the regulations of Japan, the European Union, the United States and Australia.
Some farmers own dedicated processing facilities, capable of freezing large amounts of tuna to -60oC and processing fresh tuna for transport by plane.
The frozen processing line includes the removal of fins and gill plates, cleaning and drying before being loaded onto frames for freezing. The line is designed to process up to 300 fish per hour. A -30o pre freezer ensures the fish temperature continues to reduce until all the fish are loaded into the -60o blast freezer. Within 12 hours the fish are frozen to -60oC and removed from the blast freezer, re-weighed, glazed with fresh water and loaded into a -60o container for export.
The fresh processing line includes post harvest trimming, washing and drying before being loaded into boxes with chill packs.
Tuna breeding shows 'billion-dollar' promise from The Age, Bridie Smith
July 9, 2009
In mid-2009 the Cleanseas’ Arno Bay hatchery announced that a young Southern Bluefin Tuna of 25 centimetres reached a milestone - 100 days, more than five times what captive breeders have been able to achieve previously. The project, involving the Australian Seafood Co-operative Research Centre, the Fisheries Research Development Corporation and the South Australian Research and Development Institute, aims to produce 250,000 bluefin at the hatchery outside Arno Bay on the Eyre Peninsula by 2015.
A Southern Bluefin Tuna egg spawned by Clean Seas Tuna Ltd matures to larvae (1.33 mins)